A method similar to that presented above is known e.g. from the U.S. Pat. No. 4,899,041. However, there is no indication how the working condition of the proximity switch according to the publication is checked up during its operation. It is very important to check up the working condition particularly in applications where the proximity switch is placed in connection with a moving device, such as an automatically controlled car or robot, and the proximity switch is used particularly for securing occupational safety. Consequently, it is particularly important to secure that the proximity switch works flawlessly in all conditions. It is a problem with apparatuses related to work safety that workers who move in the operation zone of e.g. an automatically operated car or robot and know that the car or robot is equipped with a proximity switch monitoring the environment of the apparatus, presume that the proximity switch works flawlessly. Thus, according to the presumption mentioned above, the workers move relatively freely in the zone of operation of the said apparatuses. Consequently, high requirements are set particularly for these applications of a proximity switch that the proximity switch is in good working order, and if it is not, the apparatus having the proximity switch must be stopped immediately after detection of a fault.
The purpose of this invention is to present a method by which the working order of the proximity switch can be checked up during the actual operation of the proximity switch in a way that no risks are induced in monitoring the situation in the detection zone. For attaining this purpose, the method according to the invention is primarily characterized in that the following steps are taken for securing the working order of the proximity switch:
at least one reflecting means is placed in the range of the beam of at least one transmitter means,
at least one controlling receiver means is placed in the range of emission from the reflecting means, and
a control circuit comprising the at least one controlling receiver means is switched on at certain intervals, whereby the processing circuit of the proximity switch is controlled on the basis of the output signal of the said at least one controlling receiver means.
By the method presented above, the working condition of the transmitter means in the optically operated proximity switch can thus be monitored and a control instruction corresponding to the control result can be transmitted to the processing circuit of the proximity switch. In other words, if the controlling receiver means receives from the reflecting means emission reflected from the transmitter means, the transmitter means is functioning and the proximity switch is in working order for this part and the protective surfaces are sufficiently clean. If this does not happen, the control circuit comprising the controlling receiver means and being connected to the processing circuit discharges an instruction by which the operations of the apparatus, such as e.g. an automatically controlled car or robot, having the proximity switch are stopped at least within the scope of occupational safety or other criteria, and e.g. a visual signal is given of the malfunction of the proximity switch.
The method according to the invention is further characterized in that the following steps are taken for checking up the working order of the proximity switch:
at least one controlling transmitter means is placed in contact with the proximity switch,
at least one reflecting means is placed in the range of the beam of the at least one controlling transmitter means,
at least one controlling transmitter means and the at least reflecting means are placed so that the at least one receiver means is placed in the range of emission from the reflecting means, and
a control circuit comprising the at least one controlling receiver means is switched on at certain intervals, whereby the processing circuit of the proximity switch is controlled on the basis of the output signal of the at least one controlling receiver means.
Consequently, the method described above can be used to check up the working condition of the receiver means monitoring the detection zone of the proximity switch and the impurity of the protective surfaces.
In the following, the invention is described in more detail with reference to the appended drawings. In the drawings,